Process of coloring granulated slate



Patented June 24, 1930 UNITED STATES PATENT OFFICE HARRY C-. FISHER, 0FCINCINNATI, OHIO,

AS SIGNOR, BY NIESNE ASSIGNMENTS, TO

PROCESS OF COLORING GRANULATED SLATE No Drawing.

My invention relates to processes for coloring slate, particularly wheredone by means of silicate.

In the making of colored roofings of desired character, of the type inwhich slate forms the exposed surface, there are two modes of procedure,one being to cut the slate into tiles, and apply them to the roofs, andthe other to crush the slate into granules, which because of its nature,are of laminated character, and roll these laminae into a mastic surfacebody so as to conceal the mastic beneath.

1 My invention applies to the latter mode of procedure, where theprovision of various colors to suit the customer are desired, because ofpeculiarities of the action of coloring matter on slate granules, andthe much greater economy in manufacture because much less coloringmatter may be used, and higher temperatures of processing are possible,thereby cutting down operating time. Thus to color-coat a slate slab andthentry to fix the adherence and accomplish changes in the color itselfby application of heat, will result in breaking up the slab, unless verycareful slow heating and cooling can be practised.

Also, all slates have an inherent color which must be overcome; and theeffect of heat on many slates is to darken their color, and all of thesefactors tend to produce a drab effect unless the coloring matter is of anature which does not permit the colors of the slate itself to besubstantially exposed. I

I have discovered that small particles of interspaced, adherent coloringmatter on a granule of slate will give a desired color effect, when suchparticles of color on a slab of slate 'will not give asatisfactory'color result at all. I have discovered that adherence ofcertain coloring matters to particles of slate crus'hed'froin the slatebody itself, will be much greater than the adherence to slabs of slate,because of a penetration factor, due to the fact that in-crushed slatethe proportion ofsurface area cutting across the planes of cleavage isvastly greater than with slabs; and penetration of pigments occursmostly parallel with the planes of cleavage.- Furthermore the generalsurface of granules 1s rougher than the surface of slabs; and thisApplication filed April 29,

1925. Serial No. 26,829.

promotes adherence of coloring both by penetration and by a mereclinging to the interstices of the surface. I

I have heretofore set forth in an application for Letters Patent SerialNo. 603,369, filed November 15, 1922, a process for imposing color ongranular slate by means of immersing the granules in a bath of sodiumsilicate of alkaline factor of .30, which I then boiled practically drywith agitation, followed by an oven treatment at 700 F. or thereabouts.This process was thus progressive and produced a colored granular massin which dried silicate as distinguished from a glass was employed asthe surface maintainmg medium. a This application for patent I haveceased to prosecute, and so far as concerns the basic principles andprogressiveness of process, the present applicationis a continuationthereof. To review briefly then the requirements of a plrocess toproduce artificially colored crushed s ate 1. The process must beeconomical both in time, labor and equipment cost and materials. 2. Itis not practical to color large pieces of slate and crush them upbecause the color in no case penetrates more than the surface of theslate.

3. Also the color penetrates across the grains, so that crushing exposesa large amount of penetration surface facilitating spreading of thecolor. 4. Because of using the slate in granular form it can be handledwith rapid heat treat ment, impossible with large pieces because theywould split up. Accordingly the process must be particularly arrangedfor economy in connection with handling a large quantity of of thesilicates, it is necessary to employ heats high enough in intensity toresult in a translucent, whitish condition of the silicate, due

probably to foaming, and hence 1n a milky or translucent glassy adherentbody of particles, which obscure the color of roasted slate granules andstill give a pleasant color effect from the color of the silicateitself.

It is a very significant fact that in the use of silicates for bindingbits of colored glass and the like to art objects, and in the use ofsilicates for impregnating porous bodies in the art of coloring marbleand the like, that the temperatures used are far below anything that Ifind to be required for effectivly imparting a permanent water repellentcoating to slate granules, for exposure to the weather on roofs, whichcoating has high adherence to the slate itself. The lack ofpenetrability of the 'sllicate into the slate bodies which I find to beresent, and the tight adherence which I gain, tend to establish that asintering action takes place not only in the silicates themselves butbetween the silicates and the slate itself, at the surface thereof.

By a slow heating over many hours below say 300 Fahrenheit, it ispossible to obtain a highly glossed, and essentially transparent film ofsilicate on any mineral body, but this coating is not of permanentnature, being gradually soluble, and susceptible to certain chemicalchanges. Slow heating is not practical in commercial coloring ofgranulated slate, as it is too expensive, so that by my improvement Iobtain economical processing, an assurance of permanence, a tighterbond, a surfacing hiding the darkened slate, practical freedom fromspotty appearance if too little of the material is used, and probably asintering action between the silicates of the coating and the silicatesof the slate.

Furthermore I have discovered that in the process of baking a solublesilicate to the requlred degree of insolubility on granulated slateparticles, the application of heat and agitation must be controlled togive the desired eflects without a balling up of the materials in such away that they will not come apart into granular form again. Thus myprocess involves progressive heat action on the particles accompanied byagitation, which first makes the surfaces coated with SlllCate dryenough to be non-adherent and then dehydrates and foams the silicate tothe proper degree of hardness and insolubility,

and resistance to atmospheric exposure. The

amount of silicate used is readily controlled of themselves .theinvention which I wish to claim in this application, in which I coverthe processes necessary for best heat treatment for slate treated withcolorin solutions, and the idea broadly of ,artifical y coloring slateby granulation and subjection to solutions or suspensions which when theslate is roasted will give an adherent coloring, particularly totreatments where silicate is involved.

The first process which I will describe relates to the use of coloredsilicates. In the action of-forming silicate, which is soluble, such assilicate of factor 1 Na O to 3.25 SiO I add during the reaction in thefurnace, according to principles adopted in making coloredglass,'sufiicient pigmenting agent, in any suitable form, to becomedistributed in the glass. By control of the proportions of sodiumcompounds in the furnace, I provide for the desired solubility of thefinal silicate, and I have found that a silicate of factor 1 Na O to3.25 SiO will serve my purposes excellently. The materials from thefurnace are treated in the usual manner to bring them to take up water,as in the usual practices of manufacture of water soluble sodiumsilicates.

The slate which is crushed in the usual manner from the form in which itis extracted from the ground, is mixed in with the silicate ande withwater, using no more water than is required. Thus to give smallproportions, which may be expanded as much as desired, I use 6 grams ofsodium silicate of the color desired, and mix this in 12 grams of water.100 grams of slate is then mixed up in the solution so as to thoroughlycoat each particle.

The coated slate is then passed through a roasting kiln, in which theproducts of combustion, or the heated air is arranged with counter-flowto the passage of the slate.

The temperature is controlled so that at the introduction of the slate,it will not be raised to a point of frothing of the silicate, until thesilicate coating on the granules has developed a surface skin. Duringthis perlod agitation is carried on as much as posslble without crushingthe granules, and such agitation as is carried on will not develop slatedust, as this, if any, appears to be held by the silicate coatings.

When the slate has passed through a zone of skin drying it moves into ahigher heat zone which causesthe silicate to whiten or to foam, andbrings it to the desired degree of insolubility (and there is someagglomeration into balls). I have found a temperature of 900 to 1000 F.and above, with a top limit so far as our practice has developed it, of1700 F. or thereabouts, will give the effect desired, namely the uniformand permanent coloring of slate granules by means of a surface coatingwithout causing any substantial adherence of the granules to each otherduring the coloring process. I find that the temperatures and conditionsnamed will produce these results satisfactorily, but I do not wish tolimit myself to this point. a Temperatures in a furnace, with relationto the material within them, as stated by me, are readings frominstruments which I have; and the proper temperatures will vary somewhatwith conditions. Essentially there should be a skin-drying accompaniedby agitation to bring the slate to a non-adhesive condition beforeanyrapid drying and particularly before any whitening or foaming isattempted.

To give full temperature ranges dependent upon the accurac of presentday -instru ments, in terms 0 the readings of which I speak 'I state as.a low limit of heat, a temperature of around 300 degrees Fahrenheit,but the heat treatment at this range will have to be very long. At 600degrees Fahrenheit maximum temperature, the better ranges of effects andmore economical processing begins to be more predominant, and thesemiopaque quality as compared to the transparent quality begins to haveconsiderable efl'ect. At 900 degrees maximum temperaturethe time factoris well cut down and the best grade of effects can be obtained, and withproper agitation, counterflow and care in use of materials, up to 1700degrees Fahrenheit is pfi'actical, using soluble silicates to begin WitThe higher heats used in the latter steps of the process more rapidlydehydrate the silicate, cause it to whiten, decrease its solubility; andit adheres tightly to the surfaces of the slate granules in smallnodules which are visible in the microscope. Also the dehydratedsilicate is of semi opaque non transparent condition so that it obscuresthe dark color of the heated slate. A mass of the colored granules willgive a true color efi'ect, although not completely coated. In theformula given the'color will be that of the silicate used as a coating.

The use of sufficient silicate with my-process would probably fully coateach granule, without resulting in permanent agglomeration of'thematerial and this has been attained in commercial practice and is theideal condition. But slate slabs covered with nodules of color will givea drab effect, while the same coating on granular slate gives a brightcolor. This is an optical-effect that is easily demonstrable, buthard-to explain.

Another way of obtaining colored silicate coatings is to use colorlesssilicate to begin with, and add the coloring matter during the slatetreatment process. Thus I may employ, giving small quantities, asbefore, 2- grams of chromic oxide, 6 grams of silicate of A factor 1 NaO to 3.25 SiO mixed with 12 cc. of water.

The slate is treated in'the same way as before and gives a bright greencolor to the final product. I

Another way of obtaining a pigmented surfacing for slate granules is toform a metal glass on the granules, instead of a dehydrated silicate.The treatment of the material is the same. Stating proportions 10 gm. oflead acetate and 10 gm. of silicate factor 1 Na O to 3.25: SiO are mixedwith 30 cc. of water. The coloring matter can be added to the mixture orthe silicate colored in the first place, as in the first example. 400gm. of slate is then mixed with the products of the reaction so as to besurface coated thereby. After dehydration the high temperatures in theroaster must be at the high end of the range heretofore given, in ordersubsequently to fuse the silicate and lead compounds, to form a leadglass. As a flux some borax can be used. This type of process is coveredby my application for patent, Serial No. 22878, filed April 13, 1925.

In any of my processes of coloring, the features of importance involvedhere are substantially the same. The granules will come out of theroaster substantially without coalescing; and if any masses are formedthese will break up, upon cooling, into the original granules. Thewhitening or frothing of thesilicate gives the clouded nature to thedehydratd substance; an amount of silicate may be used suflicient onlytocoat the granules in specks rather than completely, thus lessening thetendency to agg'lomerate, and the agitation and heat treatment isgraduated to give a preliminary skin before the frothy stage is reached,thereby avoiding permanent agglomeration even if, and this I state uponbelief, there is more than enough silicate used to fully coat eachgranule in a dehydrated or glazed condition.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is

1. A granular slate, surface-coated with a body of dehydrated solublesilicate. '2. A granular slate, surface-coated with-a body of dehydratedsoluble silicate, said silicate containing a pigmenting agent.

- 3. A anular mineral matter coated with a body of dehydrated solublesilicate, said silicate containing a pigmenting agent said mineralmaterial being of a character to withstand a roasting treatment.

4. A process of coloring. crnshedmineral matter, which consistsin'treating the crushed mineral matter with a water solution of aiialkaline silicate together with a suspended pigment, and dehydratingwithout chemically changing the silicate, to a weather permanentcondition, accompanied by agitation suflicient to prevent formation ofballs during the dehydration, said mineral material being of a characterto withstand a roasting treatment.

5. A process of coloring crushed mineral matter, which consists intreating the crushed mineral matter with a water solution of an alkalinesilicate together with a suspended pigment, and dehydrating withoutchemically changing the silicate, to a weather permanent conditionaccompanied byagitation sufiicient to prevent formation of balls duringthe dehydration, said alkaline silicate having about three times as muchSiO as it has Na O, said mineral material being of a character towithstand a roasting treatment.

6. A process of forming colored mineral matter for surfacing, whichconsists in crushing natural slate to granular form, mixing thegranuules with a wet body of soluble silicate and coloring matter, andthen treating the resultant mass with heat to permanently cause adhesionof the silicate to the granules with concurrent agitation of the mass.

der application of heat, which consists in applying coloring matter tothe granular material by means of a wet adhesive capable of dehydrationto permanent condition and then subjecting the granules to heatsuflicient to dehydrate said adhesive at a rate which causes the aqueouscondition thereof by its evolution to impart a pufiiness to the adhesivethus renderin it non-transparent said mineral granules fileing of acharacter to withstand a roasting treatment.

9. A process of forming colored material for surfacing, which consistsin crushing natural slate to granular form mixing the granules with awet body of soluble silicate in the presence 9f coloring matter, andthen treating the resultant coated granules with heat and agitation topermanently cause adhesion of the silicate to the granules, insuflicientsilicate being used to more than fully coat physically the individualgranules.

10. A process of forming colored material for surfacing, which consistsin crushing natural slate to granular form, mixing the granules with awet body of silicate in the presence of coloring matter, and thentreatingthe resultant coated granules with heat to permanently causeadhesion of the silicate to the granules, said heat treatment being atsufficiently high degree to cause whitening of thesilicate, forming anon-transparent coating, that obscures the color of the slate granulesresulting from the heat treatment.

11. A process of forming colored material for surfacing, which consistsin crushing natural slate to granular form, mixing the granules with awet body of silicate in the presence of coloring matter, and thentreating the resultant coated granules with heat to permanent-ly causeadhesion of the silicate to the granules, said heat treatment beingcontrolled to first form a skin on the coated granules, in the presenceof agitation, and then at sufficiently higher temperature to cause awhitening of the silicate.

12. A-process of forming colored material for surfacing, which consistsin crushing natural slate to granular form, mixing the granules with awet body of silicate in the presence of coloring matter, and thentreating the resultant coated granules with heat to permanently causeadhesion ofthe silicate to the granules, said heat treatment beingcontrolled to first form a skin on the coated granules in the presenceof agitation and then at sufliciently higher temperature to rapidly andthoroughly dehydrate the silicate.

13. A surfacing material comprising granulated slate, each granulecovered with a coat: ing of coloring matter in an inorganic binder, saidbinder permanently afiixed to the granule, and non-transparent.

14. A surfacing material comprising granulated slate covered withpermanently adhering interspaced particles of combined nontransparentcoloring matter and non-transparent, dehydrated soluble silicate.

15. A process of forming a mineral surfacing material for exposure tothe weather, which consists in crushing slate to granular form, wettingthe slate with a dissolved silicate in the presence of pigmentingmatter,

and roasting the slate to a temperature of not less than 600 degreesFahrenheit.

16. A process of forming mineral surfaccate in the presence ofpigmentingfmatter,

and then roasting the slate to a temperature of between 900 degreesFahrenheit, or thereabouts, and 1700 degrees Fahrenheit, or thereabouts.

17 A process for forming artificially colored granular mineral matter,which consists in coating the granular matter with a soluble silicateand coloring matter, and then passing the granules through a kiln withagitation, said kiln operated by an influx of heat in counterflow to thegranular material, for

the pur ose described said mineral matter being a character to withstanda roast- 1 ing treatment.

18. A process for forming artificially colored granular mineral matterwhich consists in coating the granular matter with a soluble silicateand coloring matter, and then passing the granules through a kiln withagitation, said kiln operated by an influx of heat in counterflow. tothe granular material, for the purpose described, the ultimatetemperature to which the granular material is raised being 600 degreeFahrenheit and upwardly said mineral matter being of a'character towithstand a roasting treatment.

HARRY C. FISHER.

